[15.02] Using Monte-Carlo Simulations to Study the Disk Structure in Cygnus X-1

Y. Yao, S. N. Zhang, X. L. Zhang, Y. X. Feng (UAH/NSSTC)

As the first dynamically determined black hole X-ray binary
system, Cygnus X-1 has been studied extensively. However,
its broad-band spectra in hard state with BeppoSAX is still
not well understood. Besides the soft excess described by
the multi-color disk model (MCD), the power-law component
and a broad excess feature above 10 keV (disk reflection
component), there is also an additional soft component
around 1 keV, whose origin is not known currently. Here we
propose that the additional soft component is due to the
thermal Comptonization process between the soft disk photon
and the warm plasma cloud just above the disk, i.e., a warm
layer. We use Monte-Carlo technique to simulate this Compton
scattering process and build several table models based on
our simulation results. With these table models, we study
the disk structure in Cygnus X-1. According to the fitting
results with our table models, the electron energy
distribution in the corona follows the Maxwellian form and
if the warm layer we proposed here is the commonly observed
outflow in x-ray binary system, the outflow velocity is
about 0.01-0.02 c in Cygnus X-1.